Trailing edge dimmer compatibility with dimmer high resistance prediction

ABSTRACT

In at least one embodiment, an electronic system includes a controller, and the controller provides compatibility between an electronic light source and a trailing edge dimmer. In at least one embodiment, the controller is capable of predicting an estimated occurrence of a trailing edge of a phase cut AC voltage and accelerating a transition of the phase cut AC voltage from the trailing edge to a predetermined voltage threshold. In at least one embodiment, the controller predicts an estimated occurrence of the trailing edge of the phase cut AC voltage on the basis of actual observations from one or more previous cycles of the phase cut AC voltage.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. §119(e) and 37C.F.R. §1.78 of U.S. Provisional Application No. 61/414,291, filed onNov. 16, 2010, and is incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to the field of electronics,and more specifically to a method and system for trailing edge dimmercompatibility with dimmer high resistance prediction.

2. Description of the Related Art

The development and use of energy efficient technologies continues to bea high priority for many entities including many companies andcountries. One area of interest is the replacement of incandescent lampswith more energy efficient lamps such as lamps based on electronic lightsources. For this description, electronic light sources are lightemitting diodes (LEDs) and compact fluorescent lamps (CFLs). Thedevelopment of electronic light source based lamps and are not withoutmany challenges. One of the challenges is developing electronic lightsource based lamps that are compatible with existing infrastructure. Thefollowing discussion focuses on LED-based lighting systems but is alsoapplicable to CFL-based lighting systems and combination LED and CFLbased lighting systems.

Many electronic systems include circuits, such as switching powerconverters that interface with a dimmer. The interfacing circuitsdeliver power to a load in accordance with the dimming level set by thedimmer. For example, in a lighting system, dimmers provide an inputsignal to a lighting system. The input signal represents a dimming levelthat causes the lighting system to adjust power delivered to a lamp,and, thus, depending on the dimming level, increase or decrease thebrightness of the lamp. Many different types of dimmers exist. Ingeneral, dimmers generate a digital or analog coded dimming signal thatindicates a desired dimming level. A trailing edge dimmer phase cuts atrailing edge of an alternating current (“AC”) supply voltage.

FIG. 1 depicts a lighting system 100 that includes a trailing edge,phase-cut dimmer 102. FIG. 2 depicts an exemplary, trailing edge phasecut voltage graph 200 and a dimmer control signal 201 associated withthe lighting system 100. Referring to FIGS. 1 and 2, the lighting system100 receives an AC supply voltage V_(IN) from voltage supply 104. Thesupply voltage V_(IN), indicated by voltage waveform 202, is, forexample, a nominally 60 Hz/110 V line voltage in the United States ofAmerica or a nominally 50 Hz/220 V line voltage in Europe. The trailingedge dimmer 102 phase cuts trailing edges, such as trailing edges 202and 204, of each half cycle of supply voltage V_(IN). Since each halfcycle of supply voltage V_(IN) is 180 degrees of the supply voltageV_(IN), the trailing edge dimmer 102 phase cuts the supply voltageV_(IN) at an angle greater than 0 degrees and less than 180 degrees. Thephase cut, input voltage V_(Φ) _(—) _(IN) to the lighting system 100represents a dimming level that causes the lighting system 100 to adjustpower delivered to a lamp 106, and, thus, depending on the dimminglevel, increase or decrease the brightness of the lamp 106. The lamp 106is an incandescent lamp and can generally be modeled as a resistor 108.

The dimmer 102 includes a timer controller 110 that generates dimmercontrol signal DCS to control a duty cycle of switch 112. The duty cycleof switch 112 is a pulse width, e.g. times t₁−t₀, divided by a period ofthe dimmer control signal, e.g. times t₃−t₀, for each cycle of thedimmer control signal DCS. The timer controller 110 converts a desireddimming level into the duty cycle for switch 112. The duty cycle of thedimmer control signal DCS is decreased for lower dimming levels, i.e.higher brightness for lamp 106, and increased for higher dimming levels.During a pulse, e.g. pulse 206 and pulse 208, of the dimmer controlsignal DCS, the switch 112 conducts, i.e. is ON, and the dimmer 102enters a low resistance state. In the low resistance state of the dimmer102, the resistance of the switch 112 is, for example, less than orequal to 10 ohms. During the low resistance state of switch 112, thephase cut, input voltage V_(Φ) _(—) _(IN) tracks the input supplyvoltage V_(IN) and the dimmer 102 transfers a dimmer current i_(DIM) tothe lamp 106.

When the timer controller 110 causes the pulse of the dimmer controlsignal 206 to end, the dimmer control signal 206 turns the switch 112OFF, which causes the dimmer 102 to enter a high resistance state, i.e.turns OFF. In the high resistance state of the dimmer 102, theresistance of the switch 112 is, for example, greater than 1 kohm. Thedimmer 102 includes a capacitor 114, which charges to the supply voltageV_(IN) during each pulse of the timer control signal DCS. In both thehigh and low resistance states of the dimmer 102, the capacitor 114remains connected across the switch 112. When the switch 112 is OFF andthe dimmer 102 enters the high resistance state, the voltage V_(C)across capacitor 114 decays, e.g. between times t₁ and t₂ and betweentimes t₄ and t₅. The rate of decay is a function of the amount ofcapacitance C of capacitor 114 and the dimmer current i_(DIM) that istransferred through the resistance R of lamp 108. Equation [1]represents the relationship between the capacitance C of capacitor 114,the dimmer current i_(DIM), and the rate of decay dV_(Φ) _(—) _(IN)/dtof the phase cut, input voltage V_(Φ) _(—) _(IN):

i _(DIM) =C·dV _(Φ) _(—) _(IN) /dt   [1]

The resistance value R of lamp 106 is relatively low and permits a highenough value of the dimmer current i_(DIM) to allow the phase cut, inputvoltage V_(Φ) _(—) _(IN) to decay to a zero crossing, e.g. at times t₂and t₅, before the next pulse of the dimmer control signal DCS.

Trailing edge dimmers, such as trailing edge dimmer 102, have somefavorable characteristics. For example, trailing edge dimmer 102 doesnot have an abrupt voltage increase when the dimmer 102 begins toconduct, e.g. at times t₀ and t₃, and has a decaying decrease when thedimmer 102 enters the high resistance state. Thus, harmonic frequenciesare lower, and the dimmer 102 generates less electromagneticinterference.

As previously discussed, electronic light sources have a higher energyefficiency than incandescent lamps of comparable light out. Thus,electronic light sources are being retrofitted into existinginfrastructure that includes trailing edge dimmers, such as trailingedge dimmer 102. An electronic light source has lower power requirementsand, thus, less dimmer current i_(DIM) is transferred to the electroniclight sources. Thus, in accordance with Equation [1] for a smallerdimmer current i_(DIM), the decay rate dV_(Φ) _(—) _(IN)/dt is less. Ifthe decay rate dV_(Φ) _(—) _(IN)/dt is too low, the phase cut, inputvoltage V_(Φ) _(—) _(IN) does not reach a zero crossing prior to abeginning of a next cycle of the supply voltage V_(IN). Failure to reacha zero-crossing can cause some trailing edge dimmers to malfunction.

FIG. 3 depicts a lighting system 300 that includes the trailing edgedimmer 102 and LED(s) 302. The dimmer 102 functions as previouslydescribed and provides a phase cut, input voltage V_(Φ) _(—) _(IN) and adimmer current to a full bridge diode rectifier 304. The rectifier 304provides the phase cut, rectified voltage V_(Φ) _(—) _(R) to a powerconverter 306. The power converter 306 respectively converts the phasecut, rectified voltage V_(Φ) _(—) _(R) and the rectified input currenti_(R) into an approximately constant output voltage V_(OUT) and anoutput current i_(OUT). The output current i_(OUT) adjusts with thedimming level indicated by the phase angle of the phase cut, inputvoltage V_(Φ) _(—) _(IN) and is approximately constant for any givendimming level.

The controller 308 includes a current controller 310 to control thetransfer of current i_(R) to the power converter 306 and regulate thepower delivered to the LED(s) 302. The LED(s) require substantially lesspower to provide the equivalent light output of an incandescent bulb.For example, the LED(s) 302 use 4 W of power to provide the equivalentlight output of a 60 W incandescent bulb. The output voltage V_(OUT) isgenerally boosted by the power converter 306 to, for example, 400V.Since the power P provided to the LED(s) 302 is approximatelyP=V_(OUT)·i_(OUT), a maximum current i_(R) transferred to the powerconverter 306 is typically only 50 mA, which is less than theapproximately 545 mA maximum current drawn by a 60 W bulb from a 110 Vsupply input voltage V_(IN). Thus, the decay time dV_(Φ) _(—) _(IN)/dtfor the lighting system 300 increases in accordance with Equation [1].The controller 308 includes a comparator 312 to detect trailing edges,such as trailing edges 314 and 316, of the phase cut, rectified voltageV_(Φ) _(—) _(R).

Detection of the trailing edge of the phase cut, rectified voltage V_(Φ)_(—) _(R) is not a simple task. The trailing edges of rectified inputvoltage V_(ΦR) _(—) _(IN) at times t₁ and t₄ are generally noisy and maycontain other distortions. To detect the trailing edges, the controller308 utilizes a comparator 312 to detect the trailing edge at a morestable portion of the phase cut, rectified voltage V_(Φ) _(—) _(R). Thecomparator 312 receives the phase cut, rectified voltage V_(Φ) _(—) _(R)or a scaled version of the phase cut, rectified voltage V_(Φ) _(—) _(R)at an inverting input of the comparator 312. The comparator 312 comparesthe phase cut, rectified voltage V_(Φ) _(—) _(R) with a fixed, trailingedge detection voltage threshold, such as +20V, and generates a trailingedge detection signal TE_DETECT. The trailing edge detection signalTE_DETECT signal is a logical 0 prior to detection of a trailing edge ofphase cut, rectified voltage V_(Φ) _(—) _(R) and transitions to alogical 1 upon detection of the trailing edge. Once the trailing edgedetection signal TE_DETECT indicates detection of the trailing edge, thecurrent controller 310 increases a transfer of current i_(DIM) throughthe dimmer 102 to increase the rate of decay dV_(Φ) _(—) _(IN)/dt and,thus, increase the rate of decay of the phase cut, rectified voltageV_(Φ) _(—) _(R) at, for example times t₂ and t₄. Increasing the rate ofdecay at times t₂ and t₅ helps ensure that the phase cut, rectifiedvoltage V_(Φ) _(—) _(R) reaches a zero crossing prior to a beginning ofa next cycle of the phase cut, rectified voltage V_(Φ) _(—) _(R). Thetrailing edge detection threshold value is set low enough to avoidprematurely detecting a trailing edge. However, because the rate ofdecay dV_(Φ) _(—) _(IN)/dt is greater for electronic light sources, thelow value of the trailing edge detection threshold also means that thetrailing edge might not be detected before a zero crossing of the phasecut, rectified voltage V_(Φ) _(—) _(R) for large phase angles.Increasing the value of the trailing edge detection threshold can resultin transferring an unnecessary amount of current from the voltage supply104.

It is desirable to improve compatibility with trailing edge dimmers.

SUMMARY OF THE INVENTION

In one embodiment of the present invention, an apparatus includes acontroller to provide compatibility between a lamp and a trailing edgedimmer. The controller is capable to predict an estimated occurrence ofa high resistance state of the trailing edge dimmer. The high resistancestate occurs when the trailing edge dimmer begins phase cutting analternating current (AC) voltage signal. The controller is furthercapable to operate in a high current mode based on the estimatedpredicted occurrence of the high resistance state of the trailing edgedimmer. The controller is also capable to operate in a low impedancemode after the AC voltage signal reaches a low voltage threshold.

In a further embodiment of the present invention, a method to providecompatibility between a lamp and a trailing edge dimmer includespredicting an estimated occurrence of a high resistance state of thetrailing edge dimmer. The high resistance state occurs when the trailingedge dimmer begins phase cutting an alternating current (AC) voltagesignal. The method further includes operating a controller of at least apower converter in a high current mode based on the estimated predictedoccurrence of the high resistance state of the trailing edge dimmer. Themethod also includes operating the controller in a low impedance modeafter the AC voltage signal reaches a low voltage threshold.

In another embodiment of the present invention, an apparatus includes acontroller that is a capable to predict an estimated occurrence of ahigh resistance state of a trailing edge dimmer. The high resistancestate occurs when the trailing edge dimmer begins phase cutting analternating current (AC) voltage signal of a phase cut AC voltage. Thecontroller is further capable to accelerate a transition of the ACvoltage from the trailing edge to a predetermined voltage threshold.

In a further embodiment of the present invention, a method includespredicting an estimated occurrence of a high resistance state of atrailing edge dimmer. The high resistance state occurs when the trailingedge dimmer begins phase cutting an alternating current (AC) voltagesignal of a phase cut AC voltage. The method further includesaccelerating a transition of the AC voltage from the trailing edge to apredetermined voltage threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood, and its numerousobjects, features and advantages made apparent to those skilled in theart by referencing the accompanying drawings. The use of the samereference number throughout the several figures designates a like orsimilar element.

FIG. 1 (labeled prior art) depicts a lighting system that includes atrailing edge dimmer.

FIG. 2 (labeled prior art) depicts a dimmer control signal and voltagewaveform associated with the trailing edge dimmer of FIG. 1.

FIG. 3 (labeled prior art) depicts a lighting system that includes atrailing edge dimmer 102 and LED(s).

FIG. 4 depicts a lighting system that includes a controller thatprovides compatibility between the trailing edge dimmer and anelectronic light source.

FIG. 5 depicts exemplary voltage and current waveforms during operationof the lighting system of FIG. 4.

FIG. 6 depicts an exemplary trailing edge compatibility operational flowchart that represents one embodiment of providing compatibility betweenthe trailing edge dimmer and electronic the light source of FIG. 4.

FIG. 7 depicts a lighting system that represents one embodiment of thelighting system of FIG. 4.

FIG. 8 depicts a zero crossing and active period detector.

FIG. 9 depicts a current control module.

DETAILED DESCRIPTION

In at least one embodiment, an electronic system includes a controller,and the controller provides compatibility between an electronic lightsource and a trailing edge dimmer. In at least one embodiment, thecontroller is capable of predicting an estimated occurrence of atrailing edge of a phase cut AC voltage and accelerating a transition ofthe phase cut AC voltage from the trailing edge to a predeterminedvoltage threshold. The terms “predict” and derivatives thereof, such as“predicting” and “prediction” mean to declare or indicate in advance.Thus, in at least one embodiment, predicting an estimated occurrence ofa trailing edge of a phase cut AC voltage declares or indicates inadvance the estimated occurrence of the trailing edge of the phase cutAC voltage. In at least one embodiment, the controller predicts anestimated occurrence of the trailing edge of the phase cut AC voltage onthe basis of actual observations from one or more previous cycles of thephase cut AC voltage.

In at least one embodiment, to provide compatibility between a trailingedge dimmer and an electronic light source, the controller predicts anestimated occurrence of a high resistance state of the trailing edgedimmer. The trailing edge of a phase cut AC voltage begins when atrailing edge dimmer enters a high resistance state. Thus, the highresistance state occurs when the trailing edge dimmer begins phasecutting an alternating current (AC) voltage signal. Based on theprediction of the estimated occurrence of the high resistance state ofthe trailing edge dimmer, the controller is capable of and configured tofurther operate in a high current mode to increase a transfer of currentfrom the trailing edge dimmer. Operating in the high current modeincreases a decay rate of the phase cut AC voltage and, in at least oneembodiment, ensures that the phase cut AC voltage reaches a low voltagethreshold prior to beginning another cycle. Once the phase cut ACvoltage reaches the low voltage threshold, the controller is capable ofand configured to operate in a low impedance mode to hold the phase cutAC voltage at or below the low voltage threshold.

FIG. 4 depicts a lighting system 400 that includes a controller 402 thatprovides compatibility between the trailing edge dimmer 404 and thelight source 410. The trailing edge dimmer 404 can be any trailing edgedimmer, such as trailing edge dimmer 102, that phase cuts a trailingedge of the input supply voltage V_(IN) from voltage supply 104. Thefull-bridge diode rectifier 408 rectifies the phase cut, input voltageV_(Φ) _(—) _(IN) to generate the phase cut, rectified voltage V_(Φ) _(—)_(R). The power converter 406 receives the phase cut, rectified voltageV_(Φ) _(—) _(R) and the rectified current i_(R) generates an outputvoltage V_(OUT) and an output current i_(OUT). The output voltageV_(OUT) and the output current i_(OUT) provide power for the lightsource 410. In at least one embodiment, the light source 410 is anelectronic light source that includes one or more LEDs, one or moreCFLs, or a combination of one or more LEDs and one or more CFLs. Thepower converter 406 can be any type of power converter and can include,for example, a boost converter, a buck converter, a boost-buckconverter, or a Cúk converter.

FIG. 5 depicts exemplary voltage and current waveforms 500 duringoperation of the lighting system 400. FIG. 6 depicts an exemplarytrailing edge compatibility operational flow chart 600 that representsone embodiment of providing compatibility between the trailing edgedimmer 404 and the light source 410. Referring to FIGS. 4, 5, and 6, thephase cut, rectified voltage V_(Φ) _(—) _(R) has an active period from afirst zero crossing to the second zero crossing of each cycle. Thewaveforms 500 depict a series of active periods T_(A)(n)-T_(A)(n−N) ofthe phase cut, rectified voltage V_(Φ) _(—) _(R), where n is an integerindex and N is an integer greater than or equal to one. The “active timeperiod T_(A)(n−X)” refers to the portion of the phase cut AC voltagethat is not equal to approximately zero for “X” ranging from 0 to N. Inat least one embodiment, the controller 402 predicts an estimated activetime period T_(A)(n)_(EST) of the n^(th) cycle of the phase cut,rectified voltage V_(Φ) _(—) _(R) that spans from a first approximatezero crossing at time t_(ZC)(n)₁ until the next approximate zerocrossing t_(ZC)(n)₂ of the active time period T_(A)(n). T_(A)(n)_(EST)represents the predicted estimate of the active time period T_(A)(n) forthe present n^(th) cycle

In at least one embodiment, controller 402 includes a trailing edgedimmer high resistance state predictor 412 to predict the estimatedactive time period T_(A)(n)_(EST) of the n^(th) cycle using the actualmeasured active time periods T_(A)(n−1) through T_(A)(n−N) of N previouscycle(s) of the phase cut, rectified voltage V_(Φ) _(—) _(R), where N isan integer greater than or equal to 1. The trailing edge high resistancestate predictor 412 senses the phase cut, rectified voltage V_(Φ) _(—)_(R) at node 414. Each active time period T_(A)(n−X) equals the timebetween a first zero crossing t_(ZC)(n−X)₁ and the second zero crossingt_(ZC)(n−X)₂ of the (n−X)^(th) cycle of the rectified input voltageV_(ΦR) _(—) _(IN). Thus, in at least one embodiment, in operation 602,the trailing edge high resistance state predictor 412 detects the timebetween approximate zero crossings t_(ZC)(n−X)₁ and t_(ZC)(n−X)₂ of eachcycle of the phase cut, rectified voltage V_(Φ) _(—) _(R) to determinethe active periods T_(A)(n−X) of the phase cut, rectified voltage V_(Φ)_(—) _(R) for X ranging from 1 to N.

In operation 603, the trailing edge high resistance state predictor 412predicts an estimated active period T_(A)(n)_(EST) of nth cycle of thephase cut, rectified voltage V_(Φ) _(—) _(R). The particular algorithmfor predicting the estimated active period T_(A)(n)_(EST) is a matter ofdesign choice. In at least one embodiment, the trailing edge highresistance state predictor 412 assumes that the estimated active periodT_(A)(n)_(EST) is equal to the previous actual measured active periodT_(A)(n−1). In at least one embodiment, the trailing edge highresistance state predictor 412 utilizes an algorithm that reflects atrend of the durations of the active periods T_(A)(n−X) for the previousN cycles of the phase cut, rectified voltage V_(Φ) _(—) _(R). Forexample, in at least one embodiment, N equals 2, and the trailing edgehigh resistance state predictor 412 determines a trend in the durationsof the active periods using Equation [2] to predict the estimated n^(th)active period T_(A)(n)_(EST):

T _(A)(n)_(EST) =T _(A)(n−1)+T _(A)(n−1)−T _(A)(n−2)=2·T _(A)(n−1)−T_(A)(n−2)   [2].

In Equation [2], T_(A)(n)_(EST) represents the predicted active timeperiod for the n^(th) cycle, T_(A)(n−1) represents an approximate actualtime period for the previous (n−1) cycle, and T_(A)(n−2) represents anapproximate actual measured time period for the previous (n−2) cycle. Asdiscussed in more detail in conjunction with FIG. 8, the trailing edgehigh resistance state predictor 412 detects approximate actual zerocrossings of each active cycle of the phase cut, rectified voltage V_(Φ)_(—) _(R). From the detection of the actual zero crossings, in at leastone embodiment, the trailing edge high resistance state predictor 412determines an approximate actual active time period T_(A)(n). Thedetermined, approximate actual time period T_(A)(n) becomes theapproximate actual time period T_(A)(n−1) used in Equation [2] whenestimating the active time period for the next cycle of phase cut,rectified voltage V_(Φ) _(—) _(R) and becomes the approximate actualtime period T_(A)(n−2) used in Equation [2] when estimating the activetime period for the cycle of phase cut, rectified voltage V_(Φ) _(—)_(R) after the next cycle.

In at least one embodiment, the trailing edge high resistance statepredictor 412 segregates the odd and even cycles of the phase cut,rectified voltage V_(Φ) _(—) _(R) because the odd and even cyclescorrelate better with each other. When segregating the odd and evencycles, the trailing edge high resistance state predictor 412 determinesthe trend in the durations of the even active periods using Equation [3]to predict the estimated n^(th) active period T_(A)(n)_(EST):

T _(A)(n)_(EST) =T _(A)(n−2)+T _(A)(n−2)−T _(A)(n−4)=2·T _(A)(n−2)−T_(A)(n−4)   [3].

When segregating the odd and even cycles, the trailing edge highresistance state predictor 412 determines the trend in the durations ofthe odd active periods using Equation [4] to predict the estimated n+1active period T_(A)(n)_(EST):

T _(A)(n+1)_(EST) =T _(A)(n−1)+T _(A)(n−1)−T _(A)(n−3)=2·T _(A)(n−1)−T_(A)(n−3)   [4].

In operation 604, the trailing edge high resistance state predictor 412detects the first, approximate zero crossing t_(ZC)(n)₁ of the presentn^(th) cycle of the phase cut, rectified voltage V_(Φ) _(—) _(R). From aknown first zero crossing time t_(ZC)(n)₁ of the n^(th) cycle and thepredicted, estimated zero crossing time period T_(A)(n)_(EST), thetrailing edge high resistance state predictor 412 predicts when thesecond zero crossing time t_(ZC)(n)₂ will occur.

In operation 606, the trailing edge high resistance state predictor 412predicts an estimated occurrence of a high resistance state of thetrailing edge dimmer 404 based on the duration of n prior cycles of thephase cut, rectified voltage V_(Φ) _(—) _(R) and detection of first,approximate zero crossing t_(ZC)(n)₁ of the present n^(th) cycle. In atleast one embodiment, the trailing edge high resistance state predictor412 determines a predicted, estimated occurrence of the high resistancestate of the trailing edge dimmer 404 for the n^(th) cycle by assumingthat the occurrence of the high resistance state of the trailing edgedimmer 404 equals the predicted second zero crossing t_(ZC)(n)₂ of then^(th) cycle less an estimated decay time T_(DC)(n) of the trailing edge502 of the phase cut, rectified voltage V_(Φ) _(—) _(R) for the n^(th)cycle.

The method of obtaining the estimated decay time T_(DC)(n) is a matterof design choice. In at least one embodiment, the trailing edge highresistance state predictor 412 utilizes a pre-stored estimated decaytime T_(DC)(n), such as 180 μsec, based on a worst case value of acapacitor, such as capacitor 114 (FIG. 1), of the trailing edge dimmer404 and an amount of current i_(DIM) controlled by the current controlmodule 416. In other embodiments, the trailing edge high resistancestate predictor 412 utilizes any of a number of algorithms to determinethe estimated decay time T_(DC)(n) of the phase cut, rectified voltageV_(Φ) _(—) _(R). For example, in at least one embodiment, estimateddecay times are stored in a look-up table (not shown) for variouscapacitance values of the trailing edge dimmer 404 and the phase cutangles of phase cut, rectified voltage V_(Φ) _(—) _(R) and accessed bythe trailing edge high resistance state predictor 412. In at least oneembodiment, a value of the capacitance of the trailing edge dimmer 404is stored in an optional memory 417 of the trailing edge high resistancestate predictor 412. In at least one embodiment, the trailing edge highresistance state predictor 412 measures or determines the decay timeT_(DC)(n−1) for the previous (n−1)^(th) cycle of the phase cut,rectified voltage V_(Φ) _(—) _(R) and utilizes the decay timeT_(DC)(n−1) from the previous (n−1)^(th) cycle as the decay timeT_(DC)(n) for the present n^(th) cycle of the phase cut, rectifiedvoltage V_(Φ) _(—) _(R). In at least one embodiment, the decay times forthe light source 410 at particular phase cut angles are empiricallydetermined in a laboratory setting using actual dimmers and actual lightsources, such as LEDs and/or CFLs. The decay times of the phase cut,rectified voltage V_(Φ) _(—) _(R) are then stored in an optionalnon-volatile memory 417 via a terminal 419 of the controller 402 andutilized by the trailing edge high resistance state predictor 412 topredict the estimated occurrence of a high resistance state of thetrailing edge dimmer 404.

In at least one embodiment, the operation 606 takes into considerationthat the phase angle of the phase cut, rectified voltage V_(Φ) _(—) _(R)can decrease from cycle-to-cycle as a dimming level is decreased. Tocompensate for a potential decrease in the phase angle, the trailingedge high resistance state predictor 412 subtracts a dynamic dimminglevel compensation time T_(DDLC) from the second zero crossing timet_(ZC)(n)₂ to obtain a predicted occurrence of the high resistance stateof the dimmer at time t_(HR)(n). The value of the dynamic dimming levelcompensation time t_(DDLC) is a matter of design choice, and, in atleast one embodiment, represents the largest possible change between thepredicted estimates of the active periods T_(A)(n)_(EST) andt_(A)(n−1)_(EST). In at least one embodiment, the dynamic dimming levelcompensation time t_(DDLC) is 120 μsec. Thus, in at least oneembodiment, the predicted occurrence of the high resistance state of thedimmer t_(HR)(n) equals t_(ZC)(n)₂−(T_(DC)−T_(DDLC)). In at least oneembodiment, the dynamic dimming level compensation time t_(DDLC) is apercentage, such as 50-75%, of the decay time T_(DC)(n). The trailingedge high resistance state predictor 412 provides the HRSTATE_PREDICTIONsignal to the current control module 416 to indicate the predictedoccurrence of the high resistance state of the dimmer t_(HR)(n).

In operation 608, at the predicted occurrence of the dimmer highresistance state t_(HR)(n), the trailing edge high resistance statepredictor 412 increases an amount of dimmer current i_(DIM) transferredto the power converter 406 through the trailing edge dimmer 404. Theincrease in the dimmer current i_(DIM) decreases the decay time T_(DC)and, thus, accelerates transition of the trailing edge of the n^(th)cycle of the phase cut, rectified voltage V_(Φ) _(—) _(R) to apredetermined threshold voltage value. In at least one embodiment, thepredetermined voltage threshold is in the range between 0 and 65V. Inthe exemplary depiction of the current i_(R), which is a rectifiedversion of the dimmer current i_(DIM), the current i_(R) tracks thephase cut, rectified voltage V_(Φ) _(—) _(R) until the predictedoccurrence of the dimmer high resistance state t_(HR)(n). At thepredicted occurrence of the dimmer high resistance state t_(HR)(n), thecurrent control module 416 increases the current i_(R) transferredthrough the trailing edge dimmer 404 to the power converter 406 to atrailing accelerator current value i_(R) _(—) _(ACCEL) than normaloperation.

The particular value of the trailing accelerator current value i_(R)_(—) _(ACCEL) is a matter of design choice. Increasing the trailingaccelerator current value i_(R) _(—) _(ACCEL) decreases the decay timeT_(DC) and increases the dimming range of the lighting system 400.Decreasing the trailing accelerator current value i_(R) _(—) _(ACCEL)increases the decay time T_(DC) and decreases the dimming range of thelighting system 400. The dimming range of the lighting system 400 isincreased because the range of phase cut angles, which correlate todimming levels, is increased while still assuring that the phase cut,rectified voltage V_(Φ) _(—) _(R) reaches a zero crossing prior to thenext zero crossing. However, increasing the value of the trailingaccelerator current value i_(R) _(—) _(ACCEL) also potentially increasesthe amount of power to be dissipated by the power converter 406.Furthermore, increasing the value of the trailing accelerator currentvalue i_(R) _(—) _(ACCEL) can result in the power converter 406 havinghigher current rated and, thus, more expensive components.

In at least one embodiment, the current control module 416 dynamicallyadjusts the value of the trailing accelerator current value i_(R) _(—)_(ACCEL) to ensure operation in discontinuous current mode (DCM) whileminimizing power dissipation. In at least one embodiment, the controller402 can switch between operation in DCM, continuous conduction mode(CCM), and/or critical conduction mode (CRM) to allow the currentcontrol module 416 flexibility in selecting the value of the trailingaccelerator current value i_(R) _(—) _(ACCEL). DCM is when the phasecut, rectified voltage V_(Φ) _(—) _(R) reaches a second zero crossingt_(AC)(n−X)₂ prior to the first zero crossing t_(ZC)(n−X+1)₁ of the nextcycle of the phase cut, rectified voltage V_(Φ) _(—) _(R). CCM is whenthe phase cut, rectified voltage V_(Φ) _(—) _(R) does not reach a secondzero crossing t_(ZC)(n−X)₂ prior to the first zero crossingt_(ZC)(n−X+1)₁ of the next cycle of the phase cut, rectified voltageV_(Φ) _(—) _(R). CRM is when the second zero crossing t_(ZC)(n−X)₂ isthe same as the first zero crossing t_(ZC)(n−X+1)₁ of the next cycle ofthe phase cut, rectified voltage V_(Φ) _(—) _(R).

In at least one embodiment, the trailing accelerator current value i_(R)_(—) _(ACCEL) is 100-500% higher than the peak normal operational valueof the current i_(R). In at least one embodiment, the normal operationalcurrent peaks at approximately 100 mA, and the trailing edge acceleratorcurrent value i_(R) _(—) _(ACCEL) is approximately 500 mA. In at leastone embodiment, the power converter 406 includes one or more optionalpower dissipation circuits 418 to transfer the additional current i_(R)and dissipate power associated with the additional current i_(R).Exemplary power dissipation circuits are described in (i) U.S. patentapplication Ser. No. 13/289,845, filed Nov. 4, 2011, entitled“Controlled Power Dissipation in a Switch Path in a Lighting System”,and inventors John L. Melanson and Eric J. King, (ii) U.S. patentapplication Ser. No. 13/289,931, filed Nov. 4, 2011, entitled“Controlled Power Dissipation in a Lighting System”, and inventors JohnL. Melanson and Eric J. King, and (iii) Ser. No. 13/289,967 filed Nov.4, 2011, entitled “Controlled Power Dissipation in a Link Path in aLighting System”, and inventors John L. Melanson and Eric J. King.

In at least one embodiment, because the voltage supply 104 is able toprovide an amount of current that greatly exceeds the trailingaccelerator current value i_(R) _(—) _(ACCEL), if the dimming level and,thus, the phase angle of the phase cut, rectified voltage V_(Φ) _(—)_(R) increases rather than decreases, the trailing accelerator currentvalue i_(R) _(—) _(ACCEL) will not distort the phase cut, rectifiedvoltage V_(Φ) _(—) _(R) waveform.

In at least one embodiment, at each second zero crossing t_(ZC)(n−X)₂,the current control module 416 transfers current i_(R) through thedimmer 404 so that the power converter 406 enters a low impedance state.In at least one embodiment, the current in the low impedance state isreferred to as a glue current and is, for example, generally describedin U.S. patent application Ser. No. 12/858,164, filed Aug. 17, 2010,entitled: “Dimmer Output Emulation”, and inventor: John L. Melanson(referred to herein as “Melanson I”) and U.S. patent application Ser.No. 13/217,174, filed Aug. 24, 2011, entitled: “Multi-Mode DimmerInterfacing Including Attach State Control”, and inventors: Eric J. Kingand John L. Melanson, which are both incorporated by reference in theirentireties.

The particular implementation of the trailing edge high resistance statepredictor 412 is a matter of design choice. The trailing edge highresistance state predictor 412 can be implemented using analog, digital,or analog and digital circuits and can be implemented using discretecomponents. In at least one embodiment, the controller 402 is anintegrated circuit, and the trailing edge high resistance statepredictor 412 and current control module 416 are implemented as part ofthe integrated circuit. In at least one embodiment, the controller 402includes a processor (not shown) and a memory (not shown) to store andexecute code that implements one or more embodiments of the exemplarytrailing edge compatibility operational flow chart 600.

FIG. 7 depicts a lighting system 700, which is one embodiment of thelighting system 400. The lighting system 700 includes controller 702,which includes the trailing edge dimmer high resistance state predictor412. The trailing edge dimmer high resistance state predictor 412generates the HRSTATE_PREDICTION signal and provides theHRSTATE_PREDICTION signal to the current control module 704 to indicatethe predicted occurrence of the high resistance state of the dimmert_(HR)(n) as previously described with reference to lighting system 400.The current control module 704 controls the boost-type switching powerconverter 706 using the same current and voltage profiles as discussedwith reference to lighting system 400 and as depicted in the exemplaryvoltage and current waveforms 500 (FIG. 5). The switching powerconverter 706 includes a boost switch 707, and the current controlmodule 704 controls power factor correction and regulates the linkvoltage V_(LINK) across link capacitor 708 as, for example, described inU.S. patent application Ser. No. 11/967,269, entitled “Power ControlSystem Using a Nonlinear Delta-Sigma Modulator With Nonlinear PowerConversion Process Modeling”, filed on Dec. 31, 2007, inventor John L.Melanson (referred to herein as “Melanson I”), U.S. patent applicationSer. No. 11/967,275, entitled “Programmable Power Control System”, filedon Dec. 31, 2007, and inventor John L. Melanson (referred to herein as“Melanson II”), U.S. patent application Ser. No. 12/495,457, entitled“Cascode Configured Switching Using at Least One Low Breakdown VoltageInternal, Integrated Circuit Switch to Control At Least One HighBreakdown Voltage External Switch”, filed on Jun. 30, 2009 (“referred toherein as “Melanson III”), and inventor John L. Melanson, and U.S.patent application Ser. No. 12/174,404, entitled “Constant CurrentController With Selectable Gain”, filing date Jun. 30, 2011, andinventors John L. Melanson, Rahul Singh, and Siddharth Maru, which areall incorporated by reference in their entireties.

The switching power converter includes capacitor 710, which filters highfrequency components from rectified voltage V_(ΦR) _(—) _(IN). Gate biasvoltage V_(G) biases the gate of switch 707. The particular value of thegate bias voltage V_(G) is a matter of design choice and, for example,depends on the operational parameters of the switch 707. In at least oneembodiment, the gate bias voltage V_(G) is +12V. To control theoperation of switching power converter 108, controller 110 generates acontrol signal CS₁ to control conductivity of field effect transistor(FET) switch 707. The control signal CS₁ is a pulse width modulatedsignal. Each pulse of control signal CS₁ turns switch 707 ON (i.e.conducts), and the inductor current i_(R) increases to charge inductor712. Diode 714 prevents current flow from link capacitor 708 into switch707. When the pulse ends, the inductor 712 reverses voltage polarity(commonly referred to as “flyback”), and the inductor current i_(R)decreases during the flyback phase. The inductor current i_(R) booststhe link voltage across the link capacitor 708 through diode 714. Theswitching power converter 706 is a boost-type converter, and, thus, thelink voltage V_(LINK) is greater than the phase cut, rectified voltageV_(Φ) _(—) _(R). The load with electronic light source 716 includes, forexample, a transformer-based interface circuit to provide power to theelectronic light sources.

FIG. 8 depicts one embodiment of a zero crossing and active timedetector 800, which is used in one embodiment of the trailing edge highresistance state predictor 412 (FIG. 4) to detect the approximate valuesof zero crossings t_(ZC)(n)₁ and t_(ZC)(n)₂ of the phase cut, rectifiedvoltage V_(Φ) _(—) _(R). The zero crossing detector 800 includes acomparator 802 to compare the phase cut, rectified voltage V_(Φ) _(—)_(R) and a phase cut, rectified voltage V_(Φ) _(—) _(R) threshold value.The phase cut, rectified voltage V_(Φ) _(—) _(R) threshold value is, forexample, in the range of 0-15V. When the comparator 802 detects that thephase cut, rectified voltage V_(Φ) _(—) _(R) has transitioned to becomegreater than the phase cut, rectified voltage V_(Φ) _(—) _(R) threshold,the ZC_DETECT output signal of the comparator 802 indicates thetransition by changing from a logical 1 to a logical 0. The transitionindicates detection of the first zero crossing t_(ZC)(n)₁. Then, thetimer 804 begins counting at a frequency much greater than the frequencyof phase cut, rectified voltage V_(Φ) _(—) _(R). For example, in atleast one embodiment, the timer 804 counts at a frequency of 10 kHz orgreater. When the comparator 802 detects that the phase cut, rectifiedvoltage V_(Φ) _(—) _(R) is less than the phase cut, rectified voltageV_(Φ) _(—) _(R) threshold, the ZC_DETECT output signal of the comparator802 indicates the detection by changing from a logical 0 to a logical 1.The transition from logical 0 to logical 1 of the ZC_DETECT outputsignal indicates detection of the second zero crossing t_(ZC)(n)₂. Thetimer 804 then indicates the time between the detection of the two zerocrossings, which is the approximate actual active time T_(A)(n).

FIG. 9 depicts a current control module 900, which represents oneembodiment of a current control module 704. The current control module900 includes a controllable current source 902. The current source 902includes FETs 904 and 906, which are configured as a current mirror.Referring to FIGS. 7 and 9, in at least one embodiment, the controller908 modulates the control signal CS₁ to control current through switch707 to control power factor correction and regulate the link voltageV_(LINK) of the switching power converter 706, generate the trailingaccelerator current value i_(R) _(—) _(ACCEL), generate the lowimpedance state of the switching power converter 706, and dissipateexcess power, as previously described.

Current source 902 supplies a reference current i_(REF), which flowsthrough FET 906. In at least one embodiment, control signal CS₁ turnsboost switch 707 ON. The size of FET 904 is scaled to the size of FET906 by a scaling factor of Z. The value of the scaling factor Z is apositive number and a matter of design choice. The value of the scalingfactor Z times the value of the reference current i_(REF) sets thetrailing accelerator current value i_(R) _(—) _(ACCEL). Thus, when thetrailing edge high resistance state predictor 412 predicts theoccurrence of the high resistance state of the dimmer t_(HR)(n), thecontroller 908 causes the controllable current source 902 to transferthe trailing accelerator current value i_(R) _(—) _(ACCEL) to theswitching power converter 706.

Thus, an electronic system includes a controller, and the controllerprovides compatibility between an electronic light source and a trailingedge dimmer. In at least one embodiment, the controller is capable ofpredicting an estimated occurrence of a trailing edge of a phase cut ACvoltage and accelerating a transition of the phase cut AC voltage fromthe trailing edge to a predetermined voltage threshold.

Although embodiments have been described in detail, it should beunderstood that various changes, substitutions, and alterations can bemade hereto without departing from the spirit and scope of the inventionas defined by the appended claims.

1. An apparatus comprising: a controller to provide compatibilitybetween a lamp and a trailing edge dimmer, wherein the controller iscapable to: predict an estimated occurrence of a high resistance stateof the trailing edge dimmer, wherein the high resistance state occurswhen the trailing edge dimmer begins phase cutting an alternatingcurrent (AC) voltage signal; operate in a high current mode based on theestimated predicted occurrence of the high resistance state of thetrailing edge dimmer; and operate in a low impedance mode after the ACvoltage signal reaches a low voltage threshold. 2-40. (canceled)